There's something I'm a bit confused by. I've been reading about how E. coli can have different NADH dehydrogenase complexes (more specifically, NDH-1 and NDH-2). One major difference between the two is the fact that NDH-1 is a coupling site (so pumps out protons while transferring electrons) while NDH-2 is not; will not pump out any protons. As a result of this, the NET ATP produced will be different. What are the benefits of having the two different NDH's, though? My textbook said:

[mentions different ATP yields]. It also means E. coli has a great latitude in adjusting (delta)P generated during respiration. Since a large (delta)P can drive reversed electron transport and thus slow down oxidation of NADH and quinol, it may be an advantage to be able to direct electrons along alternate routes that bypass coupling sites and translocate fewer protons. This could ensure adequate rates of reoxidation of NADH and quinol. -- White, 2003.

Also, (delta)p = proton motive force.

I'm just a bit confused...I thought e's were just being passed from NADH to the final e' acceptor. Is the benefit of having an NDH-2 to avoid the potential loss of any more electrons (if we're dealing with reverse e' transport)? I was under the assumption that electrons aren't being extruded. Maybe I'm getting my terminology mixed up.